Minimally invasive procedures involve accessing specific sites through anatomical structures. Examples of such procedures are angioplasty, stenting, thrombolysis, where an interventional device is navigated through the vasculature to access a designated site. Navigating through branching pathways is challenging without appropriately designed steerable medical devices.
A medical device with a steerable distal portion is disclosed in U.S. Pat. No. 5,090,956, wherein the maneuverability of the distal portion is achieved by a combination of a temperature activated memory element moving in a first direction to assume a predetermined shape when heated to a predetermined temperature and a spring for yieldable urging the shape memory element in a second direction away from the first direction upon cooling of the memory element to a temperature less than the predetermined temperature, so that the memory element is moved to assume a shape other than the predetermined shape.
Multidirectional steering of such medical device can be achieved by integrating multiple temperature activated memory elements, each of them being able to assume a predetermined shape when heated to a predetermined temperature. Deflection of a device with such configuration occurs due to the mechanical equilibrium of the force generated by the first temperature activated memory element moving in a first direction to assume a predetermined shape, the restoring force of the spring and the restoring forces of the non-active memory elements. Such construction becomes complex with increasing maneuverability requirements due to the fact that the force necessary to be created by a first temperature activated memory element in order to overcome the restoring forces of the spring and the remaining non-activated memory elements is significantly large, resulting in a considerably large cross sectional area of the temperature activated memory element. This however works against miniaturization of the device, hence when a second temperature activated memory element is required to deflect the device in a second direction to assume a predetermined shape of the second temperature activated memory element, the large cross section area of the first element creates a large restoring force at its turn, which limits the bending radius of the device.